Swim fins are devices that substantially increase the surface area of the naked foot thereby increasing the propulsive force of the legs. If used properly swim fins can conserve a diver's energy and facilitate underwater movement by becoming powerful extensions of a diver's body. In fact, fins can be so effective that arms and hands are not necessarily needed for propulsion when skin or scuba diving. However, few things feel as awkward as trying to walk while wearing swim fins due to the extended length of the fins which are cumbersome and can be potentially dangerous while walking.
To overcome this problem various swim fins have been proposed which include both a swimming and walking mode. For example, U.S. Pat. No. 5,292,272 (Grim) discloses an open-heel swim fin having a pivoting fin which pivots directly at the toe of the foot pocket. However, walking is still difficult because the non-collapsible fin blade in the retracted state is positioned at a 90.degree. angle relative to the longitudinal axis of the foot which increases resistance when walking or wading in shallow water. Likewise, U.S. Pat. No. 4,981,454 (Klein) discloses an open-heel swim fin having a retractable fin blade that pivots near the arch of the foot. This pivoting allows for the fully expanded fin blade to rise above the instep of the foot where it is positioned adjacent and parallel to the leg. This prevents an awkward upright blade at the toe of the foot pocket but the large surface area of the fin blade is still in a cumbersome position which reduces flexibility while walking. U.S. Pat. No. 4,752,259 (Tackett et al.) discloses another embodiment of an open-heel model having a retractable fin wherein the surface area of the fin blade is bifurcated. The frontal end portion of the fin blade pivots upon itself either over or under the foot to facilitate walking. However, only a portion of the blade retracts leaving a substantial length of the fin blade extending longitudinally beyond the user's foot which impedes natural ambulation.
In order to avoid the disadvantages of the aforementioned shoe-fins, it has been proposed to attach a separate and removable fin blade to the shoe-like structure. For example, U.S. Pat. No. 5,041,039 (Chang et al.) discloses a detachable fin that is secured to the sole of the shoe structure by screw means. Likewise, U.S. Pat. No. 5,766,050 (Maggi) discloses a fin blade with a cup-like structure with internal locking means that fits over the toe area of a shoe-structure and seats thereto. However, in such shoe-fins the fins must be manually attached when needed and when not in use must still be transported by the user thereby defeating the purpose of easy convertibility between a swimming and walking mode.
Still further designs for swim fins have been disclosed in U.S. Pat. No. 5,242,321 (Gil) and U.S. Pat. No. 4,250,584 (Korn) wherein collapsible fins blades are provided for easy and compact transport and storage. However, these style are still not adaptable for walking, and therefore, cannot be converted between a swimming and walking mode.
Accordingly, there is a need for a more reliable amphibious swim shoe that can be worn comfortably on land with easy convertibility for swimming without the disadvantages of a cumbersome upright protruding fully extended fin blade, reduced flexibility of movement while walking, or transport of separate fin attachments for swimming.